Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene is likely to increase, due to a developing shortage of propylene. Thus, a process that uses higher alkenes instead of propylene as feed and coproduces higher ketones, rather than acetone, may be an attractive alternative route to the production of phenols.
For example, oxidation of cyclohexylbenzene (analogous to cumene oxidation) could offer an alternative route for phenol production without the problem of acetone co-production. This alternative route proceeds through cyclohexylbenzene hydroperoxide, which is cleaved to produce phenol and cyclohexanone in substantially equimolar amounts.
However, one problem in producing phenol by way of the cleavage of cyclohexylbenzene hydroperoxide is that the cyclohexanone and phenol produce an azeotropic mixture composed of 28 wt % cyclohexanone and 72 wt % phenol. Thus any attempt to separate the cleavage effluent by simple distillation results in this azeotropic mixture. Moreover, although cyclohexanone is a valuable product with a growing market, there is currently no large worldwide merchant market for cyclohexanone; most cyclohexanone is made as an intermediate and consumed on the spot. In some cases, therefore, it may be desirable to increase the amount of phenol in the product mix from the oxidation of cyclohexylbenzene or even produce all phenol with no cyclohexanone. According to the present invention, an integrated process for producing phenol from cyclohexylbenzene is provided that facilitates control of the amount of cyclohexanone in the final product.
In particular, the present invention provides a process for producing phenol by oxidation of cyclohexylbenzene to cyclohexylbenzene hydroperoxide followed by cleavage of the cyclohexylbenzene hydroperoxide, in which at least a portion of the effluent from the cleavage step is subjected to a dehydrogenation step. The dehydrogenation not only converts at least part of the cyclohexanone in the effluent portion to additional phenol but also generates hydrogen as a by-product, which can, for example, be recycled to an initial benzene hydroalkylation step for producing the cyclohexylbenzene feed. In addition, although the cleavage effluent portion subjected to the dehydrogenation step can be a substantially pure cyclohexanone fraction produced by separation of the phenol and light and heavy ends from the raw effluent, given the cost of this separation, the process can also be applied to an effluent portion containing some or all of the phenol produced in the cleavage step. In this way, the total cost of purifying the final phenol stream and, if present, the final cyclohexanone stream can be minimized.